Arches are widely used as supports for membrane roofs with long spans and no internal supports. The maximum length of clear-span arches, built with known technologies, is limited by the magnitude of stresses in the arches cross sections, due to axial compression forces and bending moments. As arch spans increase, the increase in stresses due to axial compression is linear, but the increase in flexural or bending stresses is exponential. Therefore, in order to build arches with longer spans, and also with greater material economies, their bending moments are to be reduced or preferably eliminated altogether. In theory this is possible, but only with symmetrical loading, such as uniformly distributed snow load, because the arch curve can be designed to coincide with the pressure line of such symmetrical load, in which case no flexural stresses will result in any cross section of the arch. However, in reality, natural loads on roofs are not symmetrical. Snow load may be symmetrical, but very rarely, and only for a short time, and wind load never is.
Therefore, in order to build arches with longer clear spans, and greater material economy, than what is possible with known techniques of the prior art, a novel method and apparatus is needed, which reduces or eliminates the bending moments in arches, by converting asymmetrical roof loads into symmetrical arch loads. Such method would be especially advantageous, if it also assures that the arches' loads so converted remain not only symmetrical but also equal with each other, at all times, because the pressure line of such loads is a constant curve, and if the arch curvature is designed to follow this pressure line, then the arch will be free of bending moments at all times. The purpose of this invention is to provide such method and apparatus, that eliminates bending moments from roof arches, and thereby increases the length of their maximum clear span.